3️⃣ Chem 3: Acids, Bases and Electrolysis

Acid

Substance that forms positive Hydrogen ions in aqueous solution; pH less than 7

Alkali

A soluble base that forms negative Hydroxide ions in aqueous solution; pH greater than 7

Base

Substance that can neutralise an acid (e.g., metal oxides or hydroxides)

Neutralisation Reaction

Acid + Base → Salt + Water (exothermic reaction)

Strong Acid

Acid that fully ionises in water (e.g., HCl); very low pH

Weak Acid

Acid that partially ionises in water (e.g., Ethanoic acid); pH closer to 7

Titration

Technique to find exact volume of acid needed to neutralise known volume of alkali

Electrolysis

Decomposition of an ionic compound using electrical energy

Electrolyte

Molten or dissolved ionic compound that is decomposed; must have mobile ions

Cathode

Negative electrode; where reduction occurs (ions gain electrons); attracts cations

Anode

Positive electrode; where oxidation occurs (ions lose electrons); attracts anions

Aluminium Extraction

Aluminium oxide dissolved in molten cryolite to lower melting point and save energy

Electrolysis of Aqueous Solutions

Water can break down, producing Hydrogen (cathode) and Oxygen (anode)

Product at Cathode (Aqueous NaCl)

Hydrogen gas (Sodium more reactive than Hydrogen)

Product at Anode (Aqueous NaCl)

Chlorine gas (if solution is concentrated)

Making Insoluble Salts

Mix two soluble salts → precipitation; filter, wash, dry the precipitate